1. Field of the Invention
The present invention relates to an electrodynamic permanent magnet transducer.
2. Background Information
Electrodynamic permanent magnet transducers are generally used for the non-destructive testing of workpieces by means of ultrasound. A survey of the current status of development of such electrodynamic permanent magnet systems appears in Materials Evaluation (45), October 1987, pages 1166 ff. In essence, this survey discloses the use of a permanent magnet in combination with a spiral flat coil, wherein the spiral flat coil serves as a transducer coil. Such an embodiment is known as an open magnetic system, that is, a system in which the permanent magnet is oriented with one of its pole surfaces disposed toward a surface of a workpiece to produce magnetic field lines there. As such, the magnetic field lines generally have a magnetic return path through the air.
Essentially, in the transducer coil, located between the permanent magnet and the workpiece surface, high-frequency initial pulses are generated to induce eddy currents in the surface of the workpiece to be inspected. The pulses interact with the imposed static magnetic field and thereby generate ultrasound.
A disadvantage of this known arrangement may be found in that, because only one transducer coil is installed on the side of the permanent magnet transducer to be applied onto the workpiece to be tested, only a transmission or a reception operation can be conducted, but not both simultaneously. Consequently, an arrangement consisting of two separate permanent magnet transducers would generally be necessary to use this known permanent magnet transducer for the simultaneous transmission and reception of ultrasound waves.
Further, it should be noted that, with this known permanent magnet transducer, only a portion of the total available magnetic field can generally be used for the generation of ultrasound because, in the magnetic return path through the air, only insufficiently high field densities can generally be achieved. Also, the electrical connections of this known permanent magnet transducer are generally provided by means of a coaxial cable connection located on a side portion of the housing which projects considerably beyond the peripheral area of the housing. A disadvantage of this arrangement may be found in that such a location of the coaxial cable connection may make handling of the apparatus difficult.